A recent method of cryosurgical treatment (freezing of tumors) for colon carcinoma and prostate tumors involves liquid nitrogen being pumped into a stainless steel probe that is directly inserted within the tumor. It requires heavy storage of liquid nitrogen and pumping machinery to deliver the liquid nitrogen, and a mechanism to suck out from the probe part of the supplied liquid nitrogen that evaporates into gas.
With the cryogenic temperature derived from liquid nitrogen, tumor cells and the immediately surrounding tissues are then frozen. This procedure has to be accompanied by urethral heating, as the surrounding tissues and especially the urethra are greatly at risk of being frozen.
Results of this method show shrinkage of tumors, limiting the spread of cancer, and eventually death of cancer tissues in some successful cases (Onik, G., Ultrasound Guided Hepatic Cryosurgery in the Treatment of Metastatic Colon Carcinoma, April 1990).
The probe should constantly be kept free of nitrogen gas buildup (liquid nitrogen that has evaporated into gas in the course of circulation within the probe and heat exchange with the targeted tumor) so as not to block the flow of liquid nitrogen and boil off the rest. The insulation of the probe is very critical.
Liquid nitrogen boils off easily into gas in the course of circulation within the probe and during heat exchange with the targeted tumor. It is critical to apply and maintain a sufficient coldness to the cells in order to freeze them.
This invention (consisting of methods and a device) increases the damage and death to the cancer cells in cryosurgery treatment without the heavy and costly machinery.
Method
Current cryosurgical procedure circulates liquid nitrogen within a probe directly in contact with the tumor cells, in hopes that cellular fluids will form crystals of ice which damage the cancer cells. In this invention, in its preferred embodiments, tumor cells are first bloated with water prior to freezing so as to produce not only a much greater quantity of crystals (from added water) but also much bigger and coarser crystals that are more destructive.
It makes use of the fact that water when frozen increases in volume enough to xe2x80x9ccrackxe2x80x9d or damage a closed container completely filled with water. Moreover, it has been shown that in this method through introduction of water, freezing time is shortened since targeted cells contain more pure water that is of higher freezing point than cellular fluids.
Device
Unlike other cryosurgical probes, this device in its preferred embodiments does not circulate liquid nitrogen that poses problems of gas blockage, leaks, and heavy and expensive containers and insulation materials. Instead, what we call xe2x80x9csuper-sublimatedxe2x80x9d carbon dioxide is used as the cold source. This super-sublimated carbon dioxide is formed by immersing carbon dioxide in liquid nitrogen until thermal equilibrium (equal temperature, at xe2x88x92196 xc2x0 C.) between the two is reached.
This is to lock in or store the cold temperature of liquid nitrogen. Crystal bonds of carbon dioxide are tightened tremendously when in thermal equilibrium with the liquid nitrogen.
As a result, unlike liquid nitrogen that loses its cold temperature (boils and evaporates into gas) so easily in the course of circulation within the probe and heat exchange with tumor cells, this super-sublimated carbon dioxide is more efficient. in retaining its cold temperature. Any heat absorbed is not used up to raise its temperature but is used to weaken its crystal bonds.
The cold storage then is the extremely tight molecular bonding of the super-sublimated carbon dioxide. With this mechanism, the use of super-sublimated carbon dioxide as the cold source instead of liquid nitrogen does not require heavy and costly cold storage and insulating material.
In addition heat exchange is confined only within the tumor. This probe does not directly apply its cold temperature in any surroundings other than within the tumor area.
Unlike cryoprobes in which the cold source (liquid nitrogen) passes throughout the probe, a greater portion of which is positioned outside the targeted tumor and outside the body, the cold source of this probe is confined only within the tumor. The rest of the probe preferably is made up of only highly insulating elastomer.
Thus, the cold source does not directly receive any heat from nearby tissues and environment even if the insulating material is not as highly efficient an insulator as would be ideal. With these features, nearby tissues are kept from being frozen and utilization of the cold source is optimized.